1. The Field of the Invention
The present invention relates generally to data transmission between electronic devices. More specifically, the present invention relates to interfaces for optical communication of digital video and/or audio data between digital consumer electronic devices.
2. The Relevant Technology
Digital consumer electronics, such as digital video displays, digital video disk (DVD) readers, flat screen computer monitors, high definition televisions (“HDTV”), digital plasma screens, digital audio readers, digital audio encoders and readers, digital audio amplifiers, and digital audio processing devices have become of increased popularity. As the amount of data transferred between digital components expands to accommodate the desire for greater resolution, size, and quality, the need for high speed data transfer of digital data also increases. Several standards supporting data transfer to digital consumer electronic devices have been developed, but many have not adequately addressed the high bandwidth and high resolution needs of emerging products. In addition, many of these standards exhibit several other inherent limitations. For example, two current standards implemented for transmission of digital video and/or digital audio data include the digital video interface (DVI) standard and the high definition multimedia interface (HDMI) standard. Both the HDMI standard and the DVI standard are based on transmission minimized differential signaling (TMDS), Silicon Image's high-speed, serial link technology.
DVI Technology
DVI is a display interface developed by the Digital Display Working Group (“DDWG”). The DVI specification can provide a high-speed digital connection between DVI digital source devices (e.g. DVI digital video processing devices) and DVI digital sink devices (e.g. DVI digital video display devices). One common implementation of DVI is as an interface for a computer having a video controller card and a digital display device (CRT, LCD, projector, etc) having a display controller. The DVI interface standard and description are contained within the publication entitled Digital Visual Interface, Revision 1.0, published by the Digital Display Working Group on Apr. 2, 1999, the contents of which are hereby expressly incorporated by reference herein.
DVI utilizes a high-speed serial interface and TMDS to send data to the DVI sink device (e.g. a display device). TMDS conveys data by transitioning between “on” and “off” states. An encoding algorithm uses Boolean exclusive OR (“XOR”) or exclusive NOR (“XNOR”) operations applied to minimize the transitions to avoid excessive electromagnetic interference (“EMI”) levels in the DVI cable. An additional operation is performed to balance the DC signal.
The digital DVI connector has 24 pins that can accommodate up to two TMDS links. The basic TMDS transmission line is made up of three data channels and a clock channel. Data comprises 8 bit pixels in each of three channels (R/G/B). In some instances, a pair of TMDS lines may be used to achieve higher data rates. In addition to the TMDS data channels and clock channels, the digital interface includes a 5 VDC power source, and a hot plug detect channel. The DVI-I combined digital and analog pin assignments are similar to the DVI-D digital only interface pin assignments, but further includes several pins for transmission of an analog signal.
FIG. 1 illustrates a typical flow of data from a graphics controller 120 of a DVI source device 125, such as a digital video processing device, through the TMDS links 130 and to the display controller 135 of a DVI sink device 140, such as a digital video display device. In this process, incoming 8-bit data is encoded into 10-bit transition-minimized, DC-balanced characters. The first eight bits are encoded data, and the ninth bit identifies whether the data was encoded with XOR or XNOR logic; the tenth bit is used for DC balancing.
Due to several properties of the DVI interface, DVI cables having copper electrical cables may be limited to a length of about 3-5 meters. This limited length reduces the number of potential applications that can utilize DVI cables. For example, the length limits remote placement of digital sink devices.
Typical DVI cables having copper electrical links are also limited in bandwidth and data transfer rates. DVI data rates typically range from 22.5 mega pixels per second (Mpps) to 165 Mpps (up to 1.65 Giga bits). Because TMDS conveys data by transitioning between “on” and “off” states, electromagnetic interference (“EMI”) levels in the DVI cable can limit the speed at which data may be transferred in addition to the length of the cable.
Further, although DVI is a standard interface, some digital video processors and digital video displays may be incompatible or incapable of interoperation with one another. Thus, at least in some environments, bidirectional communication for reconfiguring a digital video processor and/or digital video display would be desirable. Unfortunately, configuration data is typically not transmitted. Further, many DVI interfaces lack sufficient connectivity to transmit data (e.g. configuration data) from the digital video display to the digital video processor. As a result, a DVI source device and a DVI sink device can remain incompatible.
HDMI Technology
HDMI is backward compatible with PCs, displays, and consumer electronics devices incorporating the DVI standard. HDMI is also based on the TMDS serial link technology. HDMI technology supports standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It transmits ATSC HDTV standards and supports 8-channel digital audio with 5 giga bytes per second (Gbps) of bandwidth. The HDMI technology, functionality, and hardware is disclosed in the “High-Definition Multimedia Interface” specification Version 1.1, May 20, 2004, by HDMI Licensing, LLC, the contents of which are hereby expressly incorporated by reference in its entirety herein.
The HDMI standard can be used for transmitting digital television audiovisual signals from DVD players, set-top boxes and other audiovisual source devices to HDMI sink devices, such as television sets, projectors and other audiovisual devices. HDMI can carry multi-channel audio data and can carry standard and high definition consumer electronics video formats. Content protection technology is also available. HDMI can also carry control and status information in both directions.
Referring to FIG. 2, an HDMI block diagram is shown where a standard HDMI cable includes four differential pairs 201-204 that make up the TMDS data and clock channels, referred to collectively as HDMI TMDS links 200. These HDMI TMDS links 200 are used to carry video, audio and auxiliary data. In addition, HDMI carries a VESA DDC channel 205. The DDC channel 205 is used for configuration and status exchange between a HDMI source 210 and a HDMI sink 215. The optional CEC protocol line 220 provides high-level control functions between all of the various audiovisual products in a user's environment.
Audio, video and auxiliary data is transmitted across the three TMDS data channels 201-203. Video pixel clock data is transmitted on the TMDS clock channel 204 and is used by an HDMI receiver 230 as a frequency reference for data recovery on the three TMDS data channels 201-203. Video data is carried as a series of 24-bit pixels on the three TMDS data channels 201-203. TMDS encoding converts the 8 bits per channel into a 10 bit DC-balanced, transition minimized sequence which is then transmitted serially across the HDMI TMDS data channels 201-203 at a rate of 10 bits per pixel clock period. Video pixel rates can range from 25 MHz to 165 MHz. The video pixels can be encoded in either RGB, YCBCR 4:4:4 or YCBCR 4:2:2 formats.
In order to transmit audio and auxiliary data across the TMDS links 200, HDMI uses a packet structure. To attain higher reliability of audio and control data, this data is protected with an error correction code and is encoded using a special error reduction coding to produce the 10-bit word that is transmitted. Optionally, HDMI can carry a single such stream at sample rates up to 192 KHz or from two to four such streams (3 to 8 audio channels) at sample rates up to 96 KHz. HDMI can also carry compressed (e.g. surround-sound) streams. The DDC channel 205 is used by the HDMI source device 210 to read the HDMI sink device's 215 Enhanced Extended Display Identification Data (E-EDID) to discover the sink device's 215 configuration and/or capabilities. The HDMI source device 210 reads the sink device's 215 E-EDID and delivers only the audio and video formats that are supported by the sink device 215. In addition, the HDMI sink device 215 can detect InfoFrames and process the received audio and video data appropriately.
A digital consumer device's external HDMI connection is embodied by two specified HDMI connectors, Type A or Type B. These connectors can be attached directly to the device or can be attached via a cable adapter that is shipped with the device. The Type A connector carries all required HDMI signals, including a single TMDS link. The Type B connector is slightly larger and carries a second TMDS link, which is necessary to support very high-resolution computer displays requiring dual link bandwidth. A passive cable adapter between Type A and Type B connectors is specified.
The CEC protocol line 220 is optionally used for higher-level user functions such as automatic setup tasks or tasks typically associated with infrared remote control usage. The Type A connector carries only a single TMDS link and is therefore only permitted to carry signals up to 165 Mpps. To support signals greater than 165 Mpps, the dual-link capability of the Type B connector is used.
The input stream to the HDMI source's transmitter 235 from the HDMI source's controller 240 will contain video pixel, packet and control data. The packet data can include audio and auxiliary data and associated error correction codes. These data items are processed in a variety of ways and are presented to the HDMI source's 210 transmitter 235 as either 2 bits of control data, 4 bits of packet data or 8 bits of video data per TMDS channel. The HDMI source controller 240 encodes one of these data types or encodes a Guard Band character on any given clock cycle. The stream of TMDS characters produced by the transmitter 235 is serialized for transmission on the TMDS data channels 201-203.
These current cables and solutions, as well as others, are limited in many ways in their capabilities to carry digital video and/or digital audio signals. For example, these cables are limited in bandwidth and distance in which they can carry TMDS signals. One solution to the problem of limited length of these cables is a repeater, which is a device with a retransmission function for extension or distribution of digital video and/or audio signals from cables such as DVI and HDMI cables. The circuitry of a repeater can retrieve, equalize, amplify, and re-transmit the digital video and/or digital audio signals into another length of cable. A repeater may be capable of transmitting digital video and/or audio signals to about 25 or 35 meters in some instances. However, a repeater can be quite expensive, add additional hardware and circuitry, require additional cables for the extension, and even still be limited in distances to which the repeater can retransmit digital video and/or audio signals and limited in the bandwidth of the cables. Therefore, repeaters have not provided a desired solution to many of the problems currently experienced with these cables, but rather tried to mitigate the limitations of such cables.
Thus, for these reasons, as well as others, there is still a need to improve digital video and/or audio cables, for example, by providing cables with improved transfer rates, increase cable lengths, and/or providing for bidirectional communication for system configuration between digital electronic components.